Expression of the rabbit uteroglobin gene in pre-implantation mouse embryos

Microinjected DNA sequences under the control of a foreign promoter may be expressed as early as the two-cell stage of mouse embryonic development, provided the correct trans-acting factors are present. A frequently utilised reporter gene in these studies is the Escherichia coli (E. coli) LacZ gene, which can be placed immediately 3' to the promoter of interest and expressed in a mammalian system. In this study a 3.6 kb gene fragment containing the E. coli LacZ gene, a 5 '-flanking Kozak initiation sequence and 3'-flanking SV40 polyadenylation signal was isolated from plasmid p610ZA and ligated into the polylinker region of pSP65 to yield the plasmid pSPLacZ. Fragments of 3.3 kb (-3254/+9) and 0.4 kb (-385/+9) of uteroglobin (UG) 5'-flanking region were inserted 5' to the LacZ fragment in this pSPLacZ construct to yield the plasmids pUG3.3LacZ and pUG400LacZ. Expression of β-galactosidase from these UG promoter regions was compared to p610ZA, which contains 0.3 kb of the 5'-flanking region of the mouse heat shock promoter (HSP70) and expresses β-galactosidase in 100% of embryos tested. While p610ZA was efficiently expressed at the 2-cell stage of mouse pre-implantation development, non-expression of pUG400LacZ and pUG3.3LacZ indicated that there is a specificity in promoter usage at this stage